Measurement of the cross-section ratio sigma_{psi(2S)}/sigma_{J/psi(1S)} in deep inelastic exclusive ep scattering at HERA (1606.08652v2)
Abstract: The exclusive deep inelastic electroproduction of $\psi(2S)$ and $J/\psi(1S)$ at an $ep$ centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range $2 < Q2 < 80$ GeV$2$, $30 < W < 210$ GeV and $|t| < 1$ GeV$2$, where $Q2$ is the photon virtuality, $W$ is the photon-proton centre-of-mass energy and $t$ is the squared four-momentum transfer at the proton vertex. The data for $2 < Q2 < 5$ GeV$2$ were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb${-1}$. The data for $5 < Q2 < 80$ GeV$2$ are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb${-1}$. The decay modes analysed were $\mu+\mu-$ and $J/\psi(1S) \pi+\pi-$ for the $\psi(2S)$ and $\mu+\mu-$ for the $J/\psi(1S)$. The cross-section ratio $\sigma_{\psi(2S)}/\sigma_{J/\psi(1S)}$ has been measured as a function of $Q2, W$ and $t$. The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.